The present invention relates to a toner for heat fixing for use in electrophotographic methods arid electrostatic recording methods such as in electrophotographic copying machines and printers.
A developer to be used in an electrophotographic copying machine is, in a developing step, deposited once on an image carrier such as a photoreceptor on which, for example, an electrostatic image is formed, then, in a transfer step, transferred from the photoreceptor to a transfer paper, and fixed onto a copying paper in a fixing step. In this case, a two-component developer comprising a carrier and a toner and a one-component developer (magnetic toner or non-magnetic toner) requiring no carrier are known as the developer for developing the electrostatic image to be formed on a latent image maintaining surface thereof.
A toner contained in the developer comprises a binder resin for the non-magnetic toner, or a binder resin and magnetic particles for the magnetic toner as a main component or main components and dispersedly contains a colorant, a charge control agent and a mold releasing agent.
In most cases, a styrene-acryl type resin or a polyester type resins used as the binder resin and a raw material monomer, a polymerization starting agent and a synthetic solvent used in a step of synthesis of these resins. In some cases, amine compounds may be contained in the charge control agent as impurities. In cases that a charge control agent of quaternary ammonium salt group or the like is used and a kneading temperature for the binder resin in a kneading and dispersing step is excessively high, amine compounds may be produced by chemical reaction with other components.
As a method to be currently used for fixing the toner, heat fixing methods such as, for example, a heat roll fixing method, an oven fixing method and a flash fixing method by which the binder resin contained in the toner is melt and fixed is generally used to obtain a sufficient fixing strength even though a pressure fixing method and the like have been attempted. The heating temperature, for example, in the case of heat roll fixing method is approximately 100.degree.-220.degree. C. In this case, there has been a problem that the above-described raw material monomer and impurities remaining in the toner are vaporized with a particular offensive odor. Since lately copying machines and printers have come to be often used nearby working people in offices along with down-sizing of these equipment, various problems with respect to such odor have been discussed with keen interests. On the other hand, generation of ozone due to corona discharging which has been considered as a cause of another offensive odor produced from electrophotographic machines has been substantially eliminated by technological innovations owing to development of a corona discharger or the like in which charging of the rollers and the brush or generation of ozone are minimized. Therefore, a problem of an odor which is produced from volatile components contained in the toner during heat fixing has been, in turn, considered as a relatively serious issue.
If these impurities are chemically unstable at normal temperature, volatile substances may be further decomposed or produced from the impurities. These volatile substances contained in the toner may be a cause of an offensive odor during storage of the toner. For example, if benzoyl peroxide is used as a polymerization starting agent, benzoic acid and biphenyl which will be the sources of such offensive odor are produced from benzoyl peroxide and remain in the binder resin.
In view of the above, as disclosed, for example, in Japanese Patent Application Laid-open (KOKAI) No. 64-70765, an idea for reducing the monomers remaining in the binder resin has been proposed and moreover there has been a teaching that it should be avoided to cause the polymerization starting agent and a chain transfer agent to remain in the toner. Japanese Patent Application Laid-open (KOKAI) No. 64-88556 has disclosed a method for synthesizing the binder resin without using an emulsifier and a disperant with an object to ensure a safety with respect to an amount of charge and reduce an effect of environmental humidity and further a method for reducing the raw material monomers, the synthetic solvent and the polymerization starting agent to be contained in the binder resin by means of vacuum flushing, in addition to the problem of the odor of toner. These methods can be considered effective as the methods to reduce volatile components in the toner.
In view of the toner as a finished product, however, it is insufficient unless not only the binder resin but also volatile components derived from a colorant and the charge control agent should be noted, and all volatile components of the binder resin including those individual volatile components such as the polymerization starting agent and residual monomers should be checked. Through the toner manufacturing steps from kneading of raw materials to the final product, attentions should be paid to volatile components produced due to chemical decomposition and reactions of raw materials. Hitherto, there have been rarely observed studies as to reduction of volatile components or odor producing substances of the final toner product as a whole.
As a result of examinations to solve the above-described problems, the present inventors have found that the problem of the odor could be solved if the quantities of volatile components obtained were controlled to be less than specific values in the measurement of the quantities of all volatile components of the toner as a whole carried out by a head space method with an object to take into account the volatile components derived from both raw materials of the toner and the manufacturing steps, and have reached the present invention and the composition of components thereof.